Method for continuous casting of metal



May 14, 1963 A. J. PHILLIPS ETAL 3,089,209 METHOD FOR CONTINUOUS CASTING0F METAL Filed Jan. 6. 1960 4 Sheets-Sheet l TAT-l. 70

S 1? 0) K: qt-BERT J. INVENTOR PHILLIPS RICHARD BFHEE y 4, 1963 A. J.PHILLIPS ETAL 3,089,209

METHOD FOR CONTINUOUS CASTING OF METAL Filed Jan. 6. 1960 4 Sheets-5heet2 5 110 5 121 f6 720 V W L T 1 :Za "7 114 INVENTORS QLBEET J. PHILLiPSBY RICHARD Ema? 2am w k QTTOQN EY May 14, 1963 A. J. PHILLIPS ETALMETHOD FOR CONTINUOUS CASTING OF METAL 4 Sheets-Sheet 3 Filed Jan. 6.1960 INVENTORS QLBEET J. FHlLLrPs RICHARD BFHEE 81/25 9 S: I I? QTTOENEV May 14, 1963 A. J. PHILLIPS ETAL METHOD FOR CONTINUOUS CASTING OFMETAL.

4 Sheets-Sheet 4 Filed Jan. 6. 1960 INVENTORS QLeER-r J. HILLIPS ICHHEDBFHER HTTO ENE? United States Patent METHOD FOR CONTINUOUS CASTING 0FMETAL Albert J. Phillips, Plainfield, and Richard Baler, New

Brunswick, NJ., assignors to American smelting and Refining Company, NewYork, N.Y., a corporation of New Jersey Filed Jan. 6, 1960, Ser. No. 8947 Claims. (Cl. 22-2001) This invention relates to a process forcontinuously casting metal. More particularly, it relates to a processfor continuously casting a copper metal, especially low oxygen copper.

Broadly, the invention comprehends, in a method for continuously castingmetal in which molten metal is introduced into one end of an open endedmold and cast metal is withdrawn from the other end of the mold, theimprovement which comprises introducing a gas containing more than about40% by volume of hydrogen to that area of the mold wall at whichfreezing of the introduced molten metal commences during the castingprocedure. For best results, such hydrogen gas is continuouslvintroduced to said area of the mold.

The invention is especially useful in continuous casting procedures inwhich the molten metal is introduced into the chilled zone of an openended, vertically disposed mold and the rate of introduction of themolten metal with respect to the rate of withdrawal of the cast metal issuch as to maintain a free mold wall surface in the chill zone of themold, i.e. a portion of the chill zone mold wall extends above the levelof the metal in the mold. In such casting procedures, the molten metalcommences to freeze at the meniscus of the metal in the mold; and inaccordance with the invention, the hydrogen gas is introduced to thatarea of the mold wall in which the meniscus of the molten metal islocated.

An important advantage of the invention is that it affords a method bywhich a metal. especially a copper metal such as copper and copper basealloys and particularly low oxygen copper, can be successfullycontinuously cast either or both for longer periods and at higher speedsthan are possible in the absence of the invention. Moreover, thecastings produced by the process possess uniformly excellent surfacecharacteristics and this is a further advantage of the process. Anotherimportant advantage of the invention is that it affords a method bywhich low oxygen copper can be continuously cast for longer periods andat higher speeds than have been possible heretofore while at the sametime producing a non-porous casting having a uniform surface and aspecific gravity higher than 8.85 and readily produces a low oxygencopper of a density above 8.90 and which for all practical purposes issubstantially that of the theoretical specific gravity of copper. Theseand other advantages of the invention will become apparent from thefollowing description thereof.

In practicing the invention, such introduction of such hydrogen gas maybe accomplished in any appropriate manner. For example, the gas may beintroduced to said area by delivering it as such thereto from an outsidesource or by releasing such gas at said area in any other suitablemanner from any suitable source. For best results in casting proceduresin which the meniscus of the metal is located in the chill zone of themold, introduction of the hydrogen gas is accomplished by conducting thehydrogen gas as such from an outside source to the mold adjacent themold wall area where the incoming molten metal contacts the chilled wallof the mold. For example, the hydrogen gas may be introduced into themold cavity above the level of the metal in the mold from a perforatedring disposed over the 3,089,209 Patented May 14, 1963 mold cavity abovethe metal in the mold or from ports in the mold wall above and adjacentto the metal level intended to be maintained in the mold during thecasting procedure; or by diffusion throught the mold wall where thelatter is fabricated of a sufiiciently porous material such as, forexample, graphite. Most efficient use of the hydrogen is made when it isintroduced by diffusion through the mold wall.

In accordance with another important feature of the invention, theinstant hydrogen gas is introduced to said mold wall area in controlledamounts. Such control is effected most readily and advantageously byregulating the amount of introduced gas to obtain a surface of a desiredcharacter on the casting as is indicated on the latter as it emergesfrom the mold. in general, with the introduction of increased amounts ofthe hydrogen gas, the appearance of an irregular pattern ofirregularities on the surface of the emerging casting is indicative thatintroduction of the hydrogen gas is approaching undesirably excessiveamounts and an irregular pattern of irregularities on a major portion ofthe surface of the emerging casting indicates an undesirable excess ofthe introduced gas. An irregular pattern of irregularities saving theappearance of cold shuts or folds which are perceptible to the touch aretypical of such an irregular pattern on the surface of the casting. Onthe other hand, with the introduction of decreased amounts of thehydrogen gas, the occurrence of small visible surface scoffs on theemerging casting is indicative that the introduction of the hydrogen gasis approaching undesirably small amounts and severe sticking whichcauses deep tears in the casting indicates the use of an undesirablysmall amount of gas. In accordance with the foregoing, a further featureof the invention comprises controlling the introduction of the hydrogengas to said mold wall area to a rate which is below that at which anirregular pattern of irregularities occurs on a major portion of thesurface of the emerging casting and above that at which deep tears occurin the casting emerging from the mold.

The invention is most advantageously used in casting proceduresemploying a vertical mold in which the level of the molten metal in themold is maintained below the top of the chilled zone of the mold and thelevel of the meniscus of the molten metal in the chill zone is moved invertical reciprocal relative movement with respect to the mold wallduring the casting procedure. Such reciprocal movement of the meniscusmay be obtained by any appropriate relative movement between the moldwall and the metal therein; for example, by horizontal reciprocation ofthe sides of a segmented mold or, more preferably, by verticalreciprocation of the mold. In the best mode of operating with suchcasting procedures, the introduction of the instant gas to the mold wallarea upon which the meniscus moves is regulated to obtain regular,uniformly spaced ripples on the surface of the emerging casting.

A hydrogen gas containing any amount of hydrogen may be employed inpracticing the invention provided the gas contains more than about seasby volume of hydrogen. Preferably. the gas contains at least by volumeof hydrogen and most preferably is a substantially pure hydrogen gassuch as is available commercially. The concentration of the hydrogen inthe instant ga affects the amount of gas employed. In general, to obtainthe same results when the concentration of the hydrogen in the gas isdecreased, the amount of gas employed is increased and vice versa. Theamount of gas employed is also alfected by the manner in which the gasis introduced to the mold Wall area. In casting procedures in which themeniscus of the molten metal is located in the chill zone of the moldduring the casting of the metal and the hydrogen gas is introduced tothe mold cavity in the space above the metal in the mold by means of aperforated ring located above the mold, the efiiciency of this mode ofintroduction, due to dilution, or burning or both, is so low that it isdifficult, even when using a 100% hydrogen gas, to introduce the gas ata sufficient rate to obtain the above mentioned irregular pattern ofirregularities on the surface of the emerging casting. However, such asurface is readily obtainable where, in such casting procedures, theinstant gas is introduced through ports in the mold wall close to themetal meniscus and especially where the gas is diffused thereto throughthe mold wall.

In practicing the invention, it was found that the casting speed isaffected by the cross-sectional shape and size of the casting to beproduced, the presence or absence of tapers in the chill zone of themold, and the rate of reciprocation of the metal meniscus or freezingmetal in the chill zones as well as by the heat conductivity of themetal being cast and the overall heat extractive capacity of the mold.In general, the reciprocation rate is increased as the casting speed(Le. the net rate of withdrawal of the casting from the mold) isincreased and vice versa. The presence of a converging taper on the moldwall defining the mold cavity increases the heat extractive capacity ofthe mold and permits the use of higher casting speeds than wouldotherwise be possible. On the other hand, the casting speed is decreasedas the least cross-sectional linear dimension of the casting isincreased.

The invention may be practiced in any continuous metal casting procedureemploying any conventional continuous casting mold fabricated of anyconventional material. However, it is most useful in casting low oxygencopper in a mold in which the metal is cast against a graphite surface,especially a tapered graphite surface, by a procedure in which a freemold wall surface is maintained in the chill zone of the mold,especially when employing a cover of a particulate solid material on thesurface of the metal in the mold during the casting procedure, andparticularly when the meniscus of the metal in the mold during suchprocedure is moved in a reciprocal movement with respect to the moldwall during the casting of the metal in the mold. Low oxygen copper asused in the specification and claims means a copper containing less than0.015% oxygen, and includes oxygen free copper and copper which has beendeoxidized with a suitable deoxidizing agent such as, for example,calcium, lithium, boron or phosphorous.

In experimenting with the continuous casting of low oxygen copperagainst a graphite surface in a vertical mold by a procedure in whichduring the casting the meniscus of the metal was located in the chillsection of the mold, reciprocation of the meniscus with respect to themold wall was employed and a protective layer of solid particulate covermaterial was maintained on top of the metal in the mold, it was foundthat, when the introduction of the instant hydrogen gas is adjusted toprovide a regular uniformly rippled surface on the emerging casting andthereafter increased amounts of the gas are introduced, the ripplebecomes more and more coarse until a point is reached when a furtherincrease in the amount of the introduced gas causes the regular rippledsurface pattern to begin to deteriorate into an irregular pattern inthat the ripple begins to become scattered or a crazy quilt pattern ofsurface imperfections having the appearance of cold shuts or folds atdisorganized angles begins to appear on the casting. Thereafter suchdeterioration of the surface increases until a major portion of thesurface of the emerging casting is involved; and it has been found that,if, when this latter occurs, the rate of introduction of the gas isquickly reduced, the possibility of rupture of the casting in the moldis avoided. On the other hand, with introduction of decreasing amountsof the gas, the ripple gradually become more and more faint until apoint is reached at which the surface of the casting becomes glassysmooth after which small visible surface scuffs begin gradually toappear on the emerging casting followed by the gradual appearance ofsmall visible surface tears thereon due to slight sticking of thecasting in the mold. Thereafter, generally within about one hour andusually within about 15 to 30 minutes, sticking becomes so severe thatmetal casting is stopped due to rupture of the casting in the moldcaused by deep tearing of the casting therein. It has been found that,if the rate of introduction of the gas is increased after the glassysmooth surface or the small visible surface scoffs or the small visiblesurface tears appear on the casting surface, the possibility of ruptureof the casting is avoided. Accordingly, in such casting of low oxygencopper the rate of introduction of the instant hydrogen gas iscontrolled to a rate below that at which an irregular pattern ofirregularities occurs on a major portion of the casting and above thatat which rupture of the casting occurs due to deep tearing. Preferably,the introduction of the gas is controlled to a rate below that at whichsaid irregular pattern begins to occur and above that at which deeptears, more preferably above that rate at which small visible surfacetears, occur on the surface of the emerging casting, and still morepreferably above that rate at which small visible surface scuffs occurthereon and most preferably above that rate at which the surface of thecasting is glassy smooth. In the best mode of operating, theintroduction of the gas is regulated to obtain regular uniformly spacedripples on the emerging surface of the casting. For best results the gasis introduced at a rate sufiicient to maintain the regular uniformlyspaced ripples on the emerging casting surface during the entire castingprocedure.

In practicing the invention in casting low oxygen copper, no limit wasfound to the period during which the casting procedure could beconducted continuously, even when exceptionally high casting speeds wereemployed. In casting low oxygen copper in accordance with the invention,highest casting speeds were obtained with shapes in which the leastcross-sectional linear dimension was less than about 5 inches. Thus, forexample, phosphorous deoxidized copper containing less than 0.015%oxygen was readily cast into billets three inches in diameter whilecontinuously withdrawing the casting from the mold at net speeds higherthan 29 linear inches per minute and as high as 64 linear inches perminute and more. Such sustained speeds are up to 6 times faster thanthose obtainable in the absence of the invention. Moreover, the surfaceand interior characteristics of the cast billet product were of auniform high quality throughout. Similar results are obtainable withmulti-sided shapes such as cakes having a rectangular cross-sectionalarea in which the least linear dimension, i.e. the thickness, is lessthan about 5 inches. Comparable speeds are obtained with other shapesand sizes and with other metal casting procedures taking intoconsideration size, shape and heat conductivity. Preferably, inpracticing the invention with such high sustained casting speeds, theleast cross-sectiona1 linear dimension of the shape of the casting (thethickness in the case of cakes and similar shapes, and the diameter inthe case of circular shapes such as billets) is about 2 to about 5inches.

In arriving at the present invention, numerous experiments wereconducted in which attempts were made to substitute other gases for theinstant hydrogen gas. For example, attempts were made to substituteinert gases such as nitrogen and helium; reducing gases such as methane,ethane, acetylene, carbon monoxide; and oxidizing gases such as air andcarbon dioxide. No gas or gas mixture was found, other than the instanthydrogen gas, which had a beneficial effect on the operating period orthe casting speed. Thus the instant use of a hydrogen gas containingmore than about 40% by volume of hydrogen is unique and criticallyimportant in the present process.

The reason or reasons for the success of the present process are notunderstood. Normally, in continuously casting metals, particularlycopper, the presence or use of hydrogen is avoided at all costs becauseof its known detrimental effect on the physical properties of the metal.In the instant process, however, the hydrogen has the beneficial effectsdescribed herein. Moreover, so far as we are aware, the hydrogen has nodetectable affect on the composition of the metal being cast. Thus, forexample, in casting copper containing up to .015 oxygen, there was noperceptible reduction in the oxygen content of the cast copper. While wedo not wish to be bound by any particular theory, it is possible thatthe hydrogen may affect surface tension at the involved mold wall areaso as to result in the benefits obtained in practicing the invention.

The invention is further illustrated in the accompanying drawings andexamples. It should be understood, however, that the drawings andexamples are given for pur poses of illustration and the invention inits broader aspects is not limited thereto.

In the drawings:

FIG. 1 is a diagrammatic view in side elevation and partly in section ofa casting system employing the preferred mode of introducing the instanthydrogen gas to the mold;

FIG. 2 is a diagrammatic elevation in section of the mold illustrated inFIG. 1;

FIG. 3 is a half plan section taken on line 33 of FIG. 2, half of themold being omitted for simplicity of illustration;

FIG. 4 is a diagrammatic view of a portion of the mold and siphon shownin FIG. l and illustrates freezing of the metal in the mold;

FIG. 5 is a view taken on line 5-5 of FIG. 2;

FIG. 6 is a diagrammatic elevation in section illustrating analternative mode of introducing the instant hydrogen gas to the mold;

FIG. 7 is a view from the bottom of the ring shown in FIG. 6;

FIG. 8 is a diagrammatic elevation in section illustrating anotheralternative mode of introducing the instant gas to the mold;

FIG. 9 is a view taken on line 9-9 of FIG. 8;

FIG. 10 is a drawing illustrating the surface on a casting produced inaccordance with the best mode of practicing the invention; and

FIG. 11 is an enlarged view in side elevation in section furtherillustrating the surface shown in FIG. 10.

Referring now to the drawings, FIG. 1 illustrates a casting system whichis at present preferred for the continuous casting of low oxygen copper.A melting furnace (not shown) supplies holding furnace 10 with themolten metal to be cast. Furnace 10 supplied pouring ladle 11 which inturn supplies siphon 12. The latter supplies mold 13 which is mounted onplatform 14 which in turn is mounted for vertical reciprocation oncarriage 15. The casting 17 is Withdrawn from the mold by a conventionalroll drive mechanism 18 and is cut into desired lengths by aconventional cut-off mechanism, such as is illustrated by cut-oil saw19. Such conventional mechanism is disclosed in Beterton and Poland U.S.Patent No. 2,291,204, granted July 28, 1942.

Before passing to roll drive mechanism 18, the casting 17 may be passedthrough chamber 20 which may be provided with a suitable sealing gasket21. The carriage may be movable horizontally on tracks 16 from over tankto permit installation of molds of different size or shape or otherwiseprovide access to the mold. A stationary working platform (not shown)may be located on opposite sides of track 16 and at the same level onwhich workmen may walk during the casting procedure.

The holding furnace 10 shown may be an upright low frequency inductionfurnace rotatable about a horizontal axis and having a pouring spout 25.It may receive molten metal through a launder or a bull ladle (notshown) from a suitable melting furnace. The construction and operationor the pouring ladle 11 and siphon 12 illustrated in FIG. 1 aredisclosed in copending application, Serial No. 724,114, filed March 26,1958 by Richard Baler and entitled, Continuous Casting. Such a ladle andsiphon are preferred as the pouring mechanism for high speed casting,especially high speed casting of shapes in which the leastcross-sectional linear dimension is less than about 5 inches although,if desired, other pouring mechanism may be used, especially for slowcasting speeds or larger shapes. The general construction and operationof mold 13 illustrated in FIGS. 2 and 3 are also disclosed in saidcopending application in that the preferred mold 13 is provided with atleast two cooling zones, in the first of which the metal being cast iscooled solely by contact with the cooled mold walls, then by contactboth with the cooled mold wall and with water or other fluid coolant ina second zone, and preferably also solely by direct contact with thecoolant in a third zone. In addition, the mold wall defining the moldcavity preferably is tapered to converge toward the end of the mold fromwhich the casting emerges and the second cooling zone is provided withnozzles for discharging the coolant against the emerging casting at suchan angle with respect thereto as to provide a venturi action asdisclosed in said copending application.

As shown in FIGS. 1 and 4, the pouring ladle 11 may comprise an enlargedbowl 26 constituting a reservoir for the molten metal, and a trough 27which supports the siphon 12. The ladle also has a skim gate 28. Theladle 11 is supported by a mechanism which permits tilting the ladle tochange the elevation of the reservoir with respect to the siphon;raising and lowering the entire ladle without tilting it; and swivelingthe entire ladle from a position (shown in FIGS. 1 and 4) with thesiphon 12 over the mold 13 to a position over a slag pot (not shown)alongside the mold.

In the ladle supporting mechanism illustrated in FIG. 1, there isprovided an elevator cylinder 31 whose lower end is fixed; cylinder 31having a piston connected to pedestal carriage 32. Operation of elevatorcylinder 31 raises and lowers the entire pedestal carriage 32 as a unit.The pedestal 32 cariers an arcuate guide track device 33 on which ismovably mounted a ladle carriage 34. Arcuate track 33 is laid out on thearc of a circle whose center is the center of siphon cup 42.

The ladle carriage 34 carries rollers 35 which ride on the arcuate guide33. A tilting cylinder 36 connects with a cross member 37 secured to thepedestal 32; and its piston connects with the ladle carriage 34. Thepedestal carriage 32 is rotatable about the vertical axis of elevatorcylinder 31 to permit the operator to swing the ladle 11 in a horizontalplane.

Operation of elevator cylinder 31 raises and lowers the ladle 11 withouttilting it. Operation of tilting cylinder 36 causes ladle carriage 34 toride on arcuate track guide 33 and thus to tilt the ladle 11 in avertical plane about the center of siphon cup 42; this tilting may beaccomplished in any position of the ladle 11 in its arc of swing aroundthe vertical axis of elevator cylinder 31, and in any elevation ofpedestal carriage 32.

It will be understood that with the cup 42 in register with the moldcavity, when the elevator cylinder 31 reaches its lowermost position,the cup 42 is automatically at the proper level within the mold 13regardless of angle of tilt of the ladle 11. Proper positioning of thecup 42 in the mold causes the cup to be completely submerged in themolten metal when the molten metal occupies its normal position of about1 /2 inches below the top of the mold. See FIG. 4.

Any operation of the tilting cylinder 36 to tilt the ladle 11 in eitherdirection operates to change the level of the metal in the ladle and,with the pedestal carriage 32 at its lowermost position, does not changethe elevation of the cup 42 from its proper position in the mold.

Thus, with the cup 42 in its proper position in the mold, metal level inthe ladle 11 may be changed either by tilting the ladle, or by addingmetal to the ladle or by removing metal from the ladle. The control ofmetal level in the ladle is used to control rate of metal flow throughthe siphon 12. The ladle may be tilted back- Ward (i.e. carriage 34lowered) far enough to stop flow through the siphon.

To prevent loss of suction during a startingup operation, cup 42 isprovided with overflow means. As shown in FIG. 4, cup 42 has a lowerdischarge opening provided with a steatite washer or nipple 53'. Thelower end of the siphon tube 40 has three circumferentially evenlydistributed notches 54 and three corresponding lugs 55, to which theoverflow cup 42 is welded, forming three cuplike overflow openings 56.Thus, provision is made for the siphon to discharge molten metal throughboth the lower steatite opening 53 and the three cup-like overflowopenings 56.

Siphon tube 40 of siphon 12 is preferably made of stainless steel withan intermediate arched portion as shown. For melting out frozen metal incase of an accidental freeze-up, the siphon tube 40 may be provided withshroud 43 (see P16. 4). The shroud is U-shaped in cross section for thegreater part of its length and follows the arched portion of the siphontube. The shroud is suitably attached to the siphon tube in spacedrelationship thereto and is fitted into the ladle wall lining 46 wherethe siphon passes through the wall, to prevent loss of liquid metal whenpouring molten metal through the siphon. In addition, the shroud isprovided with dam 47 which closes the shroud cross-section. The forwardend of shroud 43 has an upright front wall 49 which emerges from tubularextension 50. The front wall 49 and the tubular extension 50 may have aseries of holes 51 and the lower end of the tubular extension may besqueezed around siphon tube 40 to provide a restricted passage 52 or aseries of such restricted passages, to assist in melting out a frozensiphon.

As shown in FIG. 1, mold 13 is supported by a frame 14 which isvertically oscillated by a reciprocating mechanism. A suitable primemover (omitted for simplicity) is mounted on carriage 15, whichreciprocates connecting rod 61. Rod 61 is pivoted to a series of hellcrank levers 62 on one side of the frame 14. A series of bell cranklevers 63 are pivoted to the carriage on the other side of frame 14.Links 64 and 65 pivotally connect bell crank levers 62 and 63 tooscillatory frame 14. A connecting rod 66 connects bell crank levers 62and 63. A series of guide posts 67 are supported on carriage 15, andslidably engage guides on frame 14 to insure vertical reciprocation ofthe mold in a substantially vertical straight line. Any suitable meansmay be provided to vary stroke and frequency of vertical reciprocationof the mold. For example, to vary stroke, the drive motor may have acrank arm whose length is adjustable. To vary frequency, motor speed maybe changed.

Mold 13, as shown in FIGS. 2 and 3, is a composite mold. Metal block 79provided with removable graphite sleeve 94 is mounted on bottom annularmanifold 70 by means of bottom ring 72 which is bolted to the manifoldat 73. The manifold 70 rests on suitable cross pieces forming part ofplatform 14 reciprocatably mounted on carriage 15.

Sleeve 94 may be made of any suitable commercial graphite and ismachined to the desired shape. Preferably, the interior mold surface 80is machined to provide a taper which converges toward the bottom of thesleeve although the surface 80 may, if desired, be a true cylinder. Inorder to obtain optimum heat transfer, the sleeve 94 is carefully fittedinto block 79; the contacting surfaces being cylindrical and carefullymachined so that solid-to solid contact is obtained between sleeve andblock without any fluid layer at the interface which will interfere withexcellent heat transfer.

Preferably, in molds for casting round shapes-for example, billets whichare circular in transverse cross section, sleeve 94 is made oversizewith respect to the block 79 and is assembled into the latter by forcingit axially into the block. Preferably, also, the compression fit betweenthe assembled sleeve and block is sufficiently severe to provide thesolid-to'solid, fluid-free contact at operating temperatures. Ifdesired, the sleeve 94 may be omitted and the block 79 made unitary withthe molding surface 80 machined directly into the block; such a unitarystructure being preferred in molds for casting shapes such as cakeswhich in transverse cross section are square or rectangular or for othermulti-sided shapes.

The shape of manifold 70 is in general conformity with that of block 79.At its upper and inner corner manifold 70 is provided with an extensionledge 81 facing the interior of the mold and has an inlet passage 82having a flange for connection with a pipe (not shown) which suppliesthe manifold with cold water. Additional inlet passages located atequidistant points along the outside periphery of the manifold may beprovided, if desired, for the large quantities of water supplied to themold.

The manifold 70 delivers Water to the main cooling tubes 83 disposed inpassages 96 which are bored into block 79 and to five levels of watersprays. For this purpose the manifold has a series of top holes 84; aseries of bottom holes 85; its ledge 81 has a series of drilled passages86; the ledge contains holes 78 to clear the main cooling tubes 83.

For water delivery to the top or first level sprays, block 79 isprovided with a series of horizontal radial passages containing crosstubes 88, each of the latter having a nozzle tip 89 having a downwardlydirected discharge passage disposed at an angle which is less than about30 to the vertical and preferably is about 20 thereto. The passages 88connect with elbows 90 which are connected to fittings 91 connected tothe top holes 84 in the manifold 70. The inner face of the lower portionof sleeve 94 has clearance bays below the discharge nozzles 89providing, in effect, vertical ribs or projections 92 which areavailable to support the casting while the water sprays are directedbetween the ribs onto the surface of the casting before it leaves themold. With high casting speeds, this insures cooling the surface of thecasting below the plastic range while so supported.

The second level of sprays is provided by nozzle holes 87 drilled intothe ledge 81 and connecting with the passages 86 in the manifold. Theaxes of the nozzle holes 87 also may have an angle which is less thanabout 30 with the vertical, said angle preferably being about 20. Thethird, fourth and fifth levels of sprays are provided by openings 103,104 and 105 located in cooling tubes 83 and in the return bends 93. Allof these spray openings direct water against the emerging casting in thedirections indicated by the arrows. The return bends 93 connect loweropenings 85 with inner tubes 83.

In accordance with the most preferred mode of practicing the presentinvention, mold 13 is also provided with means for diffusing the instanthydrogen gas through graphite sleeves 94 to introduce the gas to thatarea of the mold wall 80 at which freezing of the introduced metalcommences during the casting procedure. As shown in FIGS. 2, 4 and 5,the outside surface of liner 94 is provided with a plurality of machinedhorizontal grooves through 114 extending around the outside surface ofthe liner. Such grooves may be V-shaped and are suitably spaced fromeach other, preferably by a distance of about /2 inch. The horizontalgrooves are connected by a plurality of machined vertical grooves 115disposed around the outside surface of sleeve 94 and produce awafile-like pattern in the sleeve. Such vertical grooves may also beV-shaped and are suitably spaced from each other preferably also by adistance of about /2 inch. T he instant hydrogen gas from an outsidesource (not shown) is conducted through pipe preferably to the uppermosthorizontal ring 110 through at least one passage 121 machined in block79, and preferably through at least three such passages distributedequi-distantly arouid the periphery of block 79. The gas thus suppliedto the uppermost groove flows around this groove to the remaininggrooves from whence it is distributed by diffusing through the pores ofthe graphite to the inner surface area of the liner whici is embraced bythe grooves; such diffusion taking place even under slight pressureforexample, as little as V2 pound per square inch, gauge, or less. For bestresults in this mode of introduction of the gas, a sufficient number ofthe horizontal grooves are employed to insure the bracketing with suchgrooves of that area of the mold wall at which the introduced metalcommences to freeze during the process. In mold 13 the entire length ofsleeve 94 is chilled and, as illustrated in FIG. 4, the introducedmolten metal commences to freeze at the meniscus. As shown in FIG. 4, asuflicient number of horizontal grooves, preferably at least five, areemployed to accommodate reciprocation of the meniscus and also to permitchange of the mean operating level of the metal in the mold.

Alternative modes of introducing the instant hydrogen gas areillustrated in FIGS. 6 through 9. As shown in H68. 6 and 7, the gas maybe introduced to the mold Wall area at which freezing of the introducedmetal commences by conducting it from a source (not shown) to ring 125from which it is discharged into the mold cavity above the metal thereinthrough a series of downwardly directed perforations 126 of suitablesize, for example, about 0.1 inch in diameter, spaced at regularintervals around the ring, preferably about /2 inch apart.Alternatively, the gas may be introduced as illustrated in FIGS. 8 and 9by conducting it from an outside source through passage 139 drilled inblock 79 to annular channel 131 machined in the outer face of sleeve 94from which it is discharged into the mold cavity above the metal thereinthrough downwardly directed ports 132 of suitable size, for example,about .01 inch in diameter, which are drilled in the sleeve and spacedat regular intervals around the periphery thereof, preferably at /2 inchintervals.

In starting the casting system illustrmed in FIG. 1, a conventionalstarting bar of appropriate length and having a cross section of a sizeand shape conforming to that of the mold cavity defined by mold surface80 and preferably also having a conventional threaded tip of reducedsize on the top thereof is employed. The top of the starting bar isinserted into the bottom of the mold a sufiicient distance to cover theribs 92 on sleeve 94 with the lower end of the bar extending below withdrawal rolls 18 so that. as the initial molten metal is fed into themold, it freezes around the threaded tip and the frozen product ispulled downwardly and out of the mold by rolls 18.

Thereafter, the siphon 12 is primed. In priming the siphon it is firstheated at least to a dull red heat, and preferably to the melting pointof the metal being cast, with a torch. Ladle 11 hearing the thus heatedsiphon is then swiveled into a position over a slag pot and the ladle,which in the meantime has been filled with molten metal from holdingfurnace 16, is tilted forward sulficiently to bring the molten metallevel in the ladle higher than the highest part of the arched portion ofsiphon tube 4%} with the dam 47 serving to retain the molten metal,thereby causing copious flow of molten metal through siphon tube 40 andthrough lower orifice 53 and upper orifices 56 in nozzle 42.

The size of orifice 53 in nozzle 42 is governed by the flow rate desiredfor the particular mold. The relationship between the effective areas oforifice 53 and of the cross section of the siphon tube 46 is such as tobuild up sufficient head in the cup 42 to keep the level of molten metalin cup 42 above the end of the siphon tube during priming. The combinedeffective area of the overflow orifices 56 and bottom orifice 53 shouldbe greater than the effective cross sectional area of the siphon tube40, so that maximum flow and velocity are obtained in the tube 40 inorder to flush out gases. If orifice 53 is too small, the velocitythrough the siphon tube will be too low, allowing gas separation at thetop of the arch of the siphon tube and loss of siphoning action orpossible freezing of the metal in the siphon tube. It will be understoodthat by effective area is meant the area which controls the rate of flowthrough the several parts of the siphon, namely, the siphon tube 40,discharge orifice 53 and overflow orifices 56.

For example, in a siphon for feeding a three inch billet mold, the sizeof orifice 53 was not greater than of the effective area of the siphontube 40. The best operating ratio was found to be between 30% and 60%.The effective area of the overflow orifices 56 was not less than 50% ofthe effective siphon tube area. For best results, the sum of theeffective areas of orifice 53 and of the overflow orifices 56 should benearly equal to (not less than 80%), or preferably greater than, theeffective area of the siphon tube 40.

It will be understood that, if discharge orifice 53 is too small, theflow through the siphon will not be fast enough to flush entrapped gasesfrom the siphon tube. The cross section of the siphon tube at the top ofits arch should be small enough to cause the velocity of the metal flowat this point to be sufiiciently high to prevent entrapped gases fromcollecting. On the other hand, there should be sufificient flow throughthe overflow orifices 56 to seal the end of the siphon conduit,particularly when the molten metal does not wet the metal of the siphonconduit.

The function of the shroud 43 and overflow holes 51 and S2 is to remelta frozen siphon tube 40. Due to error in preheating can-sing freeze-up,or in event of a foreign body becoming lodged in the siphon tube, theflow of copper during priming may cease before full metal flow can beestablished. If this condition occurs, the ladle is tilted to anelevation permitting molten metal to flow over the dam .7 and around thesiphon tube.

Freezing can also occur between the shroud 43 and the tube 40, andprogressive melting is required to remelt this metal. This isaccomplished by allowing the molten metal to overflow the front wall 49of the shroud 43 and flow, in succession, from the holes 51 and 52 inthe front of the shroud. The frozen metal is quite rapidly remelted andin a few minutes any frozen area in the siphon tube becomes remelted andflow conditions are established.

After the siphon is primed, cooling water is circulated through mold 13flowing thercthrough in the direction indicated by the arrows in FIG. 2and discharging therefrom through orifices 89, 87, 103, 164 and intotank 20. Thereafter the tilt of ladle 11 is reduced to reduce thepriming flow of metal to a volume more suitable for starting the castingoperation, usually to a value not less than about half the flow to beemployed during the casting operation, such flow being generallyindicated by an intermittent or very small trickle through upperorifices 56 while full flow from bottom orifice 53 continues. Thenwithout changing the ladle angle of tilt and with molten metalcontinuing to flow through the siphon, the ladle, as rapidly aspossible, is swiveled into registry over mold 13 and is lowered untilsiphon tip 42 is in its normal operating position in the mold. Ifreciprocation of the mold is to be employed, reciprocation is commencedafter swiveling the siphon in registry with the mold and the latter ispartly filled. When the metal covers cup 42 and reaches its normaloperating level, usually about 1 inches below the top of the mold andgenerally no higher than about V: inch below the top of mold 13, theoperator starts withdrawal rolls 18 to withdraw the starting bar at apre-sclected reduced starting speed; the reduced priming flow of metalthrough the siphon automatically adiusting to the pro-selected startingspeed when cup 42 is submerged in the molten metal. When the operator isready, he increases the lowering rate of the starting bar to fullrunning speed and at the same time raises the liquid level in ladle 11to provide sufficient head to deliver metal at the increased rate.

When the level of the metal in the mold has reached its normal operatinglevel therein, introduction of the instant hydrogen gas is preferablybegun and continued during the casting procedure, the gas beingintroduced at a sufficient rate during the procedure to provide thesurface described earlier herein on the emerging casting. Also, whereemployed, a cover of solid material is placed in the mold on top of themetal therein when the latter has reached its normal operating level.Where the cover is comprised of discrete particles as is illustrated inFIG. 4, sufficient additional material of this type is added from timeto time during the casting procedure to provide and maintain on themetal a protective cover of substantial thickness which generally is notless than about A; inch thick.

With the high heat extractive capacity provided by a mold of the typeillustrated in FIG. 2 and with the sustained high casting speedsobtainable by practice of the present invention, the casting 17 emergingfrom the mold is red hot and is rapidly chilled by the series ofpressurized water sprays 89, 87, and 103-105, and the large volume ofwater is collected in tank 20. This water is removed at any desiredlevel as by a suitable drain line 57 and may be circulated by acirculation and pumping system, through a cooling device, and back tothe water manifold 70 on the mold 13. The intensity of cooling of mold13 is so high that, even at the sustained high casting speeds obtainablewith the present invention, the molten metal congeals practically assoon as it touches the mold wall, causing the edge of the crater shell101 (see FIG. 4) to extend substantially to the free surface 24.

In practicing the invention with a mold provided with such sprays, it isvery desirable that the sprays operate with such high velocity andproper tangential direction that the cooling is effected by warming thewater, not by generating appreciable steam. Low velocity sprays used inthe uppermost position would result in steam at sufficient pressure toforce its passage upward in the mold between the casting and mold wall.This results in shallow scalloping of the surface of the billet, if thesteam reaches the solidifying surface. Accordingly, both pressure anddirection are used to create a downward venturi action which eliminatesthis effect. Preferably, in practicing the invention with such spraysoperated to provide such venturi action, the mold is provided with ataper, most preferably employing a forced taper operation as hereinafterdescribed. Preferably also the downward direction of the first andsecond level sprays 89, 37 is suilicient to insure overall venturiaction.

it will be noted that the top level of sprays 89 applies cooling whilethe wall ribs 92 are still available to contact and support the cratershell. it will be understood that, even when shrinkage of the castingdue to cooling causes the casting to tend to lose contact with the ribs92, the ribs still fit the casting sufficicntly closely to removesubstantial amounts of heat. Thus, at the zone defined by the ribs 92,heat is removed from the casting by Contact with both liquid medium andsolid medium. In other words, the zone of cooling by contact with asolid medium overlaps the zone of cooling by a liquid medium.

Preferably, in practicing the invention, the mold, as is illustrated inFIG. 2, is provided with a taper, especially when high speed casting isemployed and particularly in the high speed casting of low oxygencopper. Where a taper is employed it may be a so-called natural taper ora forced taper.

With a natural taper the inner surface 80 of mold 13 is designed tofollow the shrinkage pattern of the casting, as it passes through themold, rather closely at any par ticulzu" linear billet speed. With sucha construction, a

slow linear casting rate which produces in the casting a well cooledcross section permits the use of a steeper mold taper (Le. at a largerangle to vertical) than a rapid linear casting rate where the shape isemerging from the mold at a higher temperature. With natural tapers, asmall but finite clearance is highly desirable between the billet andmold wall along the major length of contact in such molds.

Higher casting speeds are obtainable with forced taper and, for thisreason, a forced taper operation is preferred. In a forced taperoperation a linear casting speed is employed which, in relation to thesteepness of the mold taper, is such that the shrinkage taper on thecast product, caused by the freezing and cooling of the latter, isforceably wedged against the taper on the mold wall so as to plasticallydeform the hot tube comprising the crater shell 101 enclosing the liquidcore 162 as shown in FIG. 4.

Such a forced taper operation, in a sense, is similar to wire-drawing.It requires the establishment of a crater shell with a long and deep Vwhich extends in the mold at least as far as the mold taper therein,with a strong but plastic shell wall surrounding a soft liquid center, acombination that is readily deformed by pulling it through the taperedmold. Such conditions are readily established in a forced taperoperation due to the improved contact between shell 101 and mold wall 80which so improves the rate of heat extraction from the shell to the moldwall that the shell wall congeals sufiiciently strong and thick toresist rupture at the high operating speeds which create the deep V.

In order to obtain maximum effect throughout the operating length of themold in a forced taper operation, the angle of the mold taper at eachlevel in the mold should be steeper than the corresponding naturalshrinkage taper on the cast product caused solely by the freezing andcooling of the latter at that level. In practice, a uniform mold taperwhich extends throughout the entire length of the mold, as illustratedby the taper of surface 80 on sleeve 94 in FIG. 4, has been found tooperate satisfactorily. Such a taper has the advantage of providing theproper taper angle on that part of the mold wall surrounding the freesurface of the molten metal, regardless of variation in the level ofthis surface, thus obtaining good contact between mold Wall and cratershell even at its point of formation.

Where reciprocation is employed and especially in reciprocation of themetal meniscus in the chill zone of the mold, the reciprocation ispreferably obtained by vertical reciprocation of a vertical mold on thecasting as is illustrated in FIG. 1. in such a procedure, the amplitudeand the frequency of reciprocation of the mold is related to the crosssection being cast, the amount of taper and the casting rate. Ingeneral, higher reciprocation rates are employed with higher castingspeed. Also, in general, it has been found that the ratio ofreciprocation frequency (in number of cycles per minute), to castingspeed (in inches per minute), should be at least about eight to one.Freferably, the ratio is 1G-l4 to l and at present, a ratio of about 11to l is considered ideal, especially in casting low oxygen copper.Higher ratios may also be employed although the benefits obtained byhigher ratios are usually not warranted by the extra wear and tear onthe reciprocation mechanism. Thus, for example, in employing a ratio ofll to l, 220 cycles per minute are employed at a linear casting rate of20 inches per minute, or 440 cycles per minute at a linear casting rateof 40 inches per minute. A short stroke is generally to be preferredsince this avoids excessive clearance between mold and casting on thedownward portion of the stroke. Preferably, the stroke is about A; to Hinch; :1 stroke of "i inch being most preferred.

By stroke or cycle of a vertically reciprocated mold is meant a completeround trip movement of the mold from bottom position back to bottomposition. The movement is preferably simple harmonic, varying from zerospeed at upper and lower ends to maximum speed between the upper andlower ends of the amplitude of movement.

When, in a casting system such as is illustrated in FIG. 1, verticalreciprocation of the mold is employed in conjunction with a cover ofparticulate solid material as illustrated in FIG. 4, it is desirablethat the maximum instantaneous downward speed of the mold be greaterthan the uniform downward linear speed of the casting to provide a smallgap between mold taper and casting taper and thus to permit a controlledamount of the cover 23 to feed down the mold wall between mold and castproduct.

For best results in practicing the invention in casting proceduresemploying a cover on the top of the metal in the mold, the cover is asolid particulate material, preferably one which has free flowingcharacteristics, especially under the casting conditions. For bestresults in casting low oxygen copper against a graphite mold wall, thelayer 23 is a layer of discrete particles of carbonaceous material suchas, for example, flake graphite, lamp black, pulverized anthracite, finecarbon particles, etc., or mixtures of such material. Fine bead-likecarbon particles obtained by flash distillation of a liquid petroleummaterial such as still bottoms and known as Micronex beads arepreferred. A mixture of flake graphite and such beads, especially amixture containing at least about 25% by weight of the latter, is mostpreferred as the cover in casting low oxygen copper. Preferably, suchparticulate cover material is employed in amounts suflicient to maintaina protective blanket about /2 to 2 inches thick on the top of the metalin mold 13. It is possible to employ the cover material as a means forthe introduction of the instant hydrogen gas. For example, where theabsorption characteristics of the cover material are sufficient, suchmaterial may be suitably treated outside the mold, as for example, withan appropriate gas, to releasably provide therein the instant hydrogengas, and then adding the cover material to the mold and removing ittherefrom at a sufficient rate to release therein, under the temperatureconditions therein obtaining, the instant hydrogen gas in suflicientquantities to provide the instant results. However, such a procedure iscumbersome and is not preferred.

In practicing the invention, it is advantageous to maintain thetemperature of the molten metal introduced into the mold as close aspracticable to the freezing point of the metal inasmuch as excesssuperheat, to the extent that it exists in the molten metal, increasesthe heat extractive load on the mold and results in lower casting speedsthan would otherwise be possible in a given mold. In general, thetemperature of the molten metal introduced into the mold is preferablyless than about 200 F. above the freezing point of the metal. For bestresults in casting low oxygen copper at casting speeds above about 29inches per minute, the temperature of the metal introduced into the moldis below about 2150 F., preferably below about 210i) F., and morepreferably in the range of about 20110 to 2070 F.; a temperature ofabout 205l F. being at present considered ideal.

The invention is further illustrated in the following examples.

Example 1 Phosphorous deoxidized copper having a total oxygen content ofless than .015% oxygen was cast into billets 3 inches in diameter in thecasting system shown in FIG. 1 employing the mold illustrated in FIGS. 2and 3 except that the mold was not provided with means for introducingthe instant gas and none of the latter was used. Sleeve 94 was machinedfrom a block of commercial graphite and was sufliciently oversized sothat when inserted into copper block 79 it was under suflicientcompression to insure excellent contact between the sleeve and jacketunder the casting conditions. The sleeve was also provided with auniformly converging taper of .087 inch per linear inch of the sleevethroughout the length of inner surface to provide forced taper castingof the billets at the speed employed. The temperature of the copper fedinto the mold was maintained at about 2050 F. The level of the copper inthe mold was maintained above the top of cup 42 and about 1% inches fromthe top of the mold but was not allowed to rise to a level closer than/2 inch from the top of the mold. The mold above the level of the metaltherein was kept filled with a mixture of flake graphite and Micronexheads; the mixture containing at least 25% by weight of the latter. Inreciprocating the mold a stroke inch in length was employed and theratio of the frequency of reciproca tion in cycles per minute to castingspeed in inches per minute was eleven to one. The cooling in the mold inrelation to the casting speed employed was such as to maintain aV-shaped crater (crater 382 in FIG. 4) of molten metal in the mold whichextended just below the bottom of sleeve 94 as shown in FIG. 4. Incooling the mold, cooling water at 80 F. was introduced into manifold 82and was circulated through the mold at the rate of 600 gallons perminute.

In commencing the casting procedure a conventional starting bar wasinserted in mold 13, siphon 12 was printed, water circulation throughthe mold was initiated, the siphon was moved into pouring position,vertical reciprocation of the mold was begun, the carbonaceous covermaterial was added when the top of nozzle 42 was covered with metal, andthe casting speed was brought up to operating speed, all as describedearlier herein.

Initially, an operating speed of 40 inches per minute was employed. Thebillet emerging from the mold at the beginning of the run had a lightbut uniformly spaced ripple on its surface. As the run continued, thesurface on the emerging billet began to deteriorate, at first becomingglassy smooth after which small visible scufls began to appear on thesurface which were followed by small visible tears and thereafter thebillet began sticking in the mold to such an extent that, at the end ofthe first hour of operation, the casting procedure could not becontinued.

Thereafter, numerous experiments were made in an attempt to extend theoperating period and to maintain uniformly spaced ripples on the surfaceof the casting. In the course of such experimentation, the operatingconditions were changed to employ higher and lower temperatures in themetal introduced into the mold, higher and lower phosphorous in thecopper, higher and lower ratios of reciprocation to casting speed,diiferent levels of the metal in the mold as well as changing the metallevel during the casting procedures, increased and decreased depth ofthe carbonaceous cover 011 the metal as well as various carbonaceouscovers of different composition, increased and decreased tapers as wellas no taper, and higher and lower casting speeds. No one or combinationof these or other operating conditions were found which were successful.

Example 2 The procedure and operating conditions described in Example 1for the operating speed of 40 inches per minute were repeated exceptthat, in this instance, the instant hydrogen gas was employed. Mold 13was provided with the means for introducing the gas illustrated in FIGS.2, 4 and 5. As illustrated by the dimensions shown in N6. 4, the tophorizontal channel groove lit was located /2 inch from the top of themold and horizontal grooves 1lll14 were located below it at spacedintervals of V2 inch; lowermost groove 114 being located 2 inches fromthe top of the mold. Vertical grooves 115 extending from horizontalgroove 119 to 114 were spaced around the outside periphery of sleeve 94at intervals of /2 inch. Groove was /8 inch wide and 15 .030 inch deep.Grooves 111--l15 were .030 inch wide and .030 inch deep.

After primed siphon 12 was placed in operating position in the mold andthe introduced metal had covered cup 42, the carbonaceous cover materialmixture was added and introduction of the hydrogen gas was begun, andthereafter the casting speed was brought up to the operating speed of 40inches per minute. During the casting procedure, the level of the metalin the mold was maintained at about one and one-half inches from the topof the mold and the space in the mold above the metal was kept full withthe carbonaceous cover. As in Example 1, the ratio of reciprocationfrequency to casting speed was eleven to one and the stroke was 1 inchin length. The hydrogen gas was commercially pure hydrogen and wascontinuously introduced to the mold during the casting operation at therate of 315 cc. per minute, measured at standard conditions, i.e. roomtemperature and pressure, such total flow being approximately equallydivided through the three passages 121 spaced equidistantly about theperimeter of block 79.

The run was continued without interruption for twentytwo hours at whichtime it was stopped only because the available supply of molten metalwas exhausted; the continuous billet produced being cut into convenientlengths by saw 19 as the billet passed below withdrawal rolls 18. All ofthe surface on the continuously cast billet possessed the uniformlyspaced ripples encircling the billet as illustrated by FIGS. and 11.FIG. 10 is a scale drawing illustrating the appearance of the surface tothe naked eye. As shown in the enlarged view of FIG. 11, the ripplescomprised a valley portion 140 and a relatively flat portion or land141. Upon examination it was found that the vertical length of each landportion 141 was about four times that of the adjacent valley portion andthat approximately 11 lands occurred on each linear inch of the casting.The specific gravity of the casting was found to be 8.92. The interiorof the casting was found to be free of detectable voids and had auniform radial grain structure extending substantially to the center ofthe billet and the billet was free of center porosity and pipe. Thesevered lengths of the billet were used for the production of tubes in aconventional manner by hot piercing and subsequent cold drawing tofinished sizes and resulted in the production of tubes of superiorquality which readily met the exacting standards required of tubing foruse in air conditioning apparatus and the even more exacting standardsrequired for rolled finned tube production.

In a large number of subsequent runs under the same operatingconditions, the results were found to be exactly reproducible for allpractical purposes. No upper limit was found to the casting period andin each case the casting was stopped only when the supply of availablemolten metal was exhausted. The rippled surface and the interiorcharacteristics were the same as those obtained in the first rundescribed in this example. The specific gravity was found to be 8.92 to8.93. In further runs under the same operating conditions except thatthe ratio of reciprocation frequency to casting speed was varied from 8to l up to 14 to l and more. it was found that the results weresubstantially the same except that the number of lands 141 whichoccurred per linear inch of casting corresponded to the employed ratiobut that the width of the lands increased at the ratio decreased andvice versa. Thus. when this frequency was reduced to 8 to l, eight landsoccurred in each linear inch of the casting but the lands werecorrespondingly wider whereas when the ratio was increased to 14 to l,fourteen correspondingly narrower lands occurred per linear inch ofcasting.

Example 3 The procedure of Example 2 was repeated employing the elevento one ratio of reciprocation frequency to casting speed. After the 40inches per minute operating speed was reached, the casting was continuedfor two hours while introducing the pure hydrogen gas to the mold at the315 cc. per minute rate as described in Example 2 to produce theregular, uniformly spaced ripples on the billet surface. The rate ofintroduction of the hydrogen gas was then decreased. It was found thatas the rate of introduction was decreased, the surface of the emergingcasting gradually and progressively deteriorated. ln thus deteriorating,the ripples on the surface of the emerging billet became lighter andless pronounced until they finally disappeared and, at a rate of gasintroduction into the mold of 25 cc. per minute, the emerging surfacebecame glassy smooth. With continued decrease in the rate ofintroduction of the gas, small visible surface scuffs began to appear onthe emerging casting. The sculfs were small abraded areas which were ingeneral sequential alignment with the axis of the emerging billet; suchgenerally aligned scuffs occurring at irregular intervals around theperiphery of the casting. After the scuffs appeared, small visibleshallow surface tears, caused by slight sticking of the casting in themold, began to appear on the emerging casting surface. Thereafter thetears became progressively more deep and, thirty minutes after theinitial appearance of the small tears, sticking became so severe thatmetal casting was stopped due to deep tearing of the billet in the moldresulting in its rupture therein. As was the case with the scutfs, theshallow tears and the deep tears, were in general spaced sequentialalignment with the longitudinal axis of the billet and such alignedtears occurred at irregular intervals about the billet periphery.

Sleeve 94, which was damaged by the rupturing of the billet, wasreplaced and the run was repeated as before but in this instance therate of introduction of the gas was decreased until the emerging billetsurface became glassy smooth and thereafter the rate of introduction ofthe gas was not further decreased. An hour after the emerging billetsurface had become glassy smooth, oasting Was stopped as before due torupture of the billet.

Sleeve 94 was again replaced and the run repeated as before. In thisinstance after the emerging billet surface became glassy smooth the rateof introduction of the gas was increased to the 315 cc. per minute ratewhich was employed initially in the run and the normal uniformly spacedripple was quickly restored on the surface of the emerging casting. Therate of introduction of the gas was then reduced until the small surfacescuffs ap peared on the surface of the casting. The rate of gasintroduction was then increased to the 315 cc. per minute rate and thenormal rippled surface was quickly restored. Thereafter the rate of gasintroduction was reduced until the small visible tears appeared afterwhich the rate was returned to the 315 cc. per minute. Again the normalripple was quickly restored to the casting surface. In additional runs,such reduction and increase of the rate of introduction of the gas wasrepeated numerous times without damaging mold wall (see FIG. 2). In eachcase the surface of the emerging billet deteriorated as described andthe deteriorated surface was quickly restored to the normal uniformlyspaced ripple when the rate of introduction of the gas was restored tothat originally employed in the run.

Attempts were then made to restore the uniform rippled surface afterdeep tears were produced on the casting. The rate of introduction of thegas was reduced sufficiently to produce deep tears and was returned tothe 315 cc. per minute rate before rupture of the casting occurred. In aminor number of the attempts, the rippled surface was restored to thecasting surface when the gas rate was increased to the 315 cc. perminute rate. However, in a major number of the attempts, sticking of thedeeply torn billet caused the mold wall 80 to be scarred to such anextent that the normal ripple could not be restored and casting wasstopped due to rupture of the billet in the mold Within an hour afterthe introduction of the gas was returned to the 315 cc. per minute rate.

Sleeve 94 was again replaced and the run started and operated as beforefor two hours with the 315 cc. per minute rate of introduction of thegas. Thereafter, the rate of gas introduction was continuouslyincreased. It was found that, as the rate was increased, the surface ofthe ripple on the emerging casting became more and more coarse until, ata rate of introduction of the gas at 850 cc. per minute, the ripple onthe emerging casting began to scatter and to assume a crazy quiltpattern of surface imperfections which were perceptible to the touch andwhich had the appearance of cold shuts and folds at disorganized angles.With further increases in the rate of introduction, this irregularpattern increased until, at a rate of gas introduction of 1320 cc. perminute, it involved a major portion of the surface of the casting. Afurther increase in the rate of introduction of the gas was then made.Within five minutes thereafter, casting was stopped due to rupture ofthe billet in the mold. In repeating this run after replacing sleeve 94and starting up the system as before, it was found that higher rates ofintroduction of the gas were required to cause the irregular pattern toappear on the casting surface and to involve a major portion of thesurface therewith when more severe cooling conditions were employed inthe mold; more severe cooling being obtained in this instance by lowertemperatures in the available supply of cooling water.

In a further run sleeve 94 was replaced, the system was started and runfor the two hour period as before. Thereafter, the rate of introductionof the gas was again continuously increased and the uniformly spacedripple on the surface of the emerging casting deteriorated as before.However, when a major portion of the surface became involved with theirregular pattern above noted, the rate of introduction of the gas wasquickly reduced to the 315 cc. per minute rate initially employed andthe normal uniformly spaced ripple was restored on the surface of theemerging casting. In additional runs, such increase and reduction of therate of introduction of the gas was repeated numerous times with thesame results. Thereafter in another run, the rate of introduction of thegas was controlled to produce at will the above noted irregular patternof irregularities, the smooth surface, the small visible surface scuffsand tears, checks, and the uniformly spaced ripple, on the surface ofthe emerging casting.

Additional runs at speeds from 30 to 64 inches per minute were made; theheat extraction required of the mold at the latter speed being close tothe maximum heat extractive capacity of the mold being used. The ratioof the reciprocation frequency to the casting speed was varied from 814to 1 during these runs. No limit was found to the period during whichthe casting procedure could be conducted continuously at these speedsand it was found that the rate of introduction of the gas could becontrolled to produce at will the uniformly spaced ripple, the irregularpattern of irregularities as well as the smooth surface and the smallvisible surface scuifs and tears on the surface of the billet. Inaddition, it was found that, when the rate of introduction of the gaswas adjusted to provide the normal uniformly spaced ripples on thesurface of the casting at a given speed, the speed could thereafter bevaried over a comparatively wide range without further adjustment of therate while still maintaining such a surface on the casting. It isbelieved that the forced taper reduces or prevents loss of hydrogen tothe zone of reduced pressure in the bottom of the mold establishedtherein by the venturi effect of nozzles 89 and 87.

Example 4 The procedure of Example 2 was again repeated but in thisinstance the mold was provided with the means illustrated in FIGS. 8 and9 for introducing the hydrogen gas, employing ports 132 which were .010to .012 inch in diameter. It was found that the rate of introduction ofthe gas could be controlled to produce at will the irregular pattern ofirregularities, the smooth surface, the small visi- Example 5 Theprocedure of Example 2 was repeated employing the means illustrated inFIGS. 6 and 7 for introducing the gas; the downwardly directedperforations 126 being .010 inch in diameter. Inasmuch as the mold wasnot shielded from the atmosphere, burning of the gas occurred at the topof the mold. It was found that the rate of introduction of the gas couldbe controlled to produce at will the small visible surface scuffs andtears as well as the uniformly spaced ripple on the surface of thecasting. However, it was not possible to introduce the gas at asufficiently high rate to produce the irregular pattern ofirregularities on the emerging billet. It is believed this latter wasdue to the dilution effect of the products of combustion or air or both.

Example 6 The procedure of Example 2 was repeated employing the elevento one ratio of reciprocation frequency to casting speed. After the 40inches per minute operating speed was reached, the casting was continuedfor two hours while introducing the commercially pure hydrogen gas tothe mold as described in Example 2 to produce the normal uniformlyspaced ripple on the surface of the billet as described therein.Thereafter, the introduced hydrogen gas was progressively diluted withnitrogen gas. As the concentration of the hydrogen in the gas mixturewas decreased, no apparent change took place in the character of therippled surface until the hydrogen concentration in the gas wasreducedto about 79% by volume, thereafter the ripple became progressively morefaint. When the hydrogen concentration in the gas reached about 40% byvolume, the billet surface possessed the glassy smoothness which, asnoted in Example 3, preceded deep tearing and ultimate rupture of thecasting in the mold and it was not possible to improve the surface ofthe emerging billet with increased rates of introduction of the thusdiluted gas. The run was repeated employing helium as the diluent gasand the same results were obtained. The results from these runsillustrate the critical importance of the concentration of the hydrogenin the introduced gas in practicing the invention.

Example 7 The procedure of Example 2 was again repeated employing theeleven to one ratio of reciprocation to casting speed. After the 40inches per minute casting speed was reached, the casting procedure wascontinued for two hours while introducing the commercially pure hydrogengas to the mold at the 315 cc. per minute rate to produce the uniformlyspaced ripple on the surface of the emerging casting described inExample 2. Thereafter, an equal how of commercially pure carbon monoxidewas substituted for the commercially pure hydrogen. Within 15 minutes,the introduction of the carbon monoxide gas had to be discontinued dueto the rapid deterioration of the billet surface and introduction of thepure hydrogen gas at the rate of 315 cc. per minute was immediatelybegun to restore the normal ripple surface to the casting. The procedurewas repeated employing changes in the casting conditions as described inExample 1 as well as various rates of introduction of the carbonmonoxide in an attempt to extend the operating period. In all such teststhe introduction of the carbon monoxide had to be discontinued within 15minutes due to deterioration of the surface of the billet and no set ofoperating conditions or rates of introduction of the gas were foundwhich would enable the carbon monoxide gas to maintain the uniformlyspaced ripples on the surface of the casting provided by the use of theinstant hydrogen gas.

The foregoing procedure was repeated employing, as a substitute for thehydrogen, various gases such as, for example, nitrogen, helium, air,carbon dioxide, steam,

19 methane, ethane, propane, acetylene, etc. and mixtures thereof. inall cases introduction of the substituted gas had to be discontinuedwithin 15 minutes to one and onehalf hours and no set of operatingconditions were found which would enable a substituted gas to maintainthe uniformly spaced ripple on the surface of the casting.

In conducting the foregoing test with steam, it Was found that the steamcondensed in passage 121 and in grooves 110-115. Steam was thereforeintroduced employing the introduction means shown in FIGS. 6 and 7.Within 15 minutes introduction of the steam had to be discontinued dueto the explosion hazards arising from condensation of the steam againstthe cold mold walls. It was also noted in testing gaseous hydrocarbons,that copious amounts of carbon black were produced in the mold. Theforegoing runs were repeated employing methane, ethane, propane andacetylene as a substitute for the hydrogen gas but in each case in thisinstance the cover material was skimmed from the top of the metal beforethe introduction of these gases was begun and no cover material wasadded. With each of these gases the surface of the bare metal quicklybecame covered with carbon black. However, in all these additional runs,introduction of the gas had to be discontinued within an hour andone-half due to deterioration of the surface of the emerging billet. Thesame results were obtained when attempts were made to substitutelubricating oil for the instant hydrogen gas by adding the oil to thecover material or to the bare metal in the mold. The results from theforegoing runs in this example further illustrate the unique andcritical importance of the instant hydrogen gas in the presentinvention.

Example 8 The procedure of Example 2 was repeated employing the elevento one ratio of reciprocation frequency to casting speed. After the 40inches per minute operating speed was reached, the casting procedure wascontinued for two hours while introducing the pure hydrogen gas to themold at the 315 cc. per minute rate as described in Example 2 to producethe billet surface described therein. Thereafter, the metal level in themold was raised and lowered from the normal level of 1% inches from thetop of the mold. Higher levels caused coarsening of the rippled surfaceof the emerging billet, the effect being that obtained by an increase inrate of introduction of the gas at the normal level of 1% inches fromthe top of the mold. Lowering the level below the normal level causedthe ripple on the surface to become increasingly faint; the effect beingthat of a decrease in the rate of introduction of the gas. When themetal level was lowered to and below the lower limit of the effectivehydrogen diffusion zone in the mold (such lower limit occurring belowthe level of groove i113 and above that of groove 114 of the moldillustrated in FIG. 4), the effect was the same as that obtained when nohydrogen was introduced into the mold. These results further illustratethe critical importance of introducing the instant hydrogen gas to thatarea of the mold wall at which freezing of the introduced metalcommences.

While certain novel features of the invention have been disclosedherein, and are pointed out in the annexed claims, it will be understoodthat various omissions,

20 substitutions and changes may be made by those skilled in the artwithout departing from the spirit of the invention.

What is claimed is:

1. In a method for continuously casting copper base metal in whichmolten copper base metal is fed into the top of a vertically disposedopen-ended mold having a chill section for casting the molten metal andcast metal is withdrawn from the other end of the mold while maintainingthe level of the metal in the mold below the top of the chill section,said chill section presenting a graphite face to the metal cast therein,and the meniscus of the metal in said chill section is verticallyreciprocated with respect to the wall of the chill section, theimprovement in combination therewith which comprises feeding said moltenmetal to said chill section at a temperature which is less than about200 F. above the freezing point of the metal being cast, introducing agas containing more than about 40% by volume of hydrogen to the meniscusof the metal in the chill section during the casting procedure, andcontrolling the amount of hydrogen which is delivered to said meniscusby controlling the amount of said hydrogen delivered to the meniscusduring the casting procedure to a rate of introduction which is betweenthat rate which produces an irregular pattern of irregularities on amajor portion of the surface of the casting emerging from the mold andthat rate which produces deep tears on the surface of the emergingcasting.

2. A method according to claim 1 in which a cover is maintained abovethe molten metal being cast in the mold.

3. A method according to claim 2 in which said metal is low oxygencopper, said hydrogen gas is introduced to said meniscus beneath a coverof solid particulate material which is added to and maintained on top ofthe metal in the mold during the casting procedure in amounts sufiicientto provide a cover of said material which is not less than about A; inchthick and the casting emerging from the mold possesses a rippledsurface.

4. A method according to claim 3 in which said cover material is acarbonaceous material and the gas providing said hydrogen gas at saidmeniscus is led into the mold cavity above the metal level therein.

5. A method according to claim 3 in which said cover material is acarbonaceous material and said hydrogen gas is introduced to said metalmeniscus by diffusion through said graphite face of said mold.

6. A method according to claim 5 in which said metal is phosphorusdeoxidized copper, said hydrogen gas introduced to said meniscuscontains at least hydrogen by volume.

7. A method according to claim 6 in which said hydrogen gas issubstantially pure hydrogen gas.

References Cited in the tile of this patent UNITED STATES PATENTS2,131,307 Behredt Sept. 27, 1938 2,135,183 Junghans Nov. 1, 19382,376,518 Spence May 22, 1945 2,740,117 Smart Apr. 3, 1956 2,743,494Rossi May 1, 1956 2,871,534 Wieland Feb. 3, 1959 2,946,100 Baier et al.July 26, 1960

1. IN A METHOD FOR CONTINUOUSLY CASTING COPPER BASE METAL IN WHICH MOLTEN COPPER BASE METAL IS FED INTO THE TOP OF A VERTICALLY DISPOSED OPEN-ENDED MOLD HAVING A CHILL SECTION FOR CASTING THE MOLTEN METAL AND CAST METAL IS WITHDRAWN FROM THE OTHER END OF THE MOLD WHILE MAINTAINING THE LEVEL OF THE METAL IN THE MOLD BELOW THE TOP OF THE CHILL SECTION, SAID CHILL SECTION PRESENTING A GRAPHITE FACE TO THE METAL CAST THEREIN, AND THE MENISCUS OF THE METAL IN SAID CHILL SECTION IS VERTICALLY RECIPROCATED WITH RESPECT TO THE WALL OF THE CHILL SECTION, THE IMPROVEMENT IN COMBINATION THEREWITH WHICH COMPRISES FEEDING SAID MOLTEN METAL TO SAID CHILL SECTION AT A TEMPERATURE WHICH IS LESS THAN ABOUT 200*F. ABOVE THE FREEZING POINT OF THE METAL BEING CAST, INTRODUCING A GAS CONTAINING MORE THAN ABOUT 40% BY VOLUME OF HYDROGEN TO THE MENISCUS OF THE METAL IN THE CHILL SECTION DURING THE CASTING PROCEDURE, AND CONTROLLING THE AMOUNT OF HYDROGEN WHICH IS DELIVERED TO SAID MENISCUS BY CONTROLLING THE AMOUNT OF SAID HYDROGEN DELIVERED TO THE MENISCUS DURING THE CASTING PROCEDURE TO A RATE OF INTRODUCTION WHICH IS BETWEEN THAT RATE WHICH PRODUCES AN IRREGULAR PATTERN OF IRREGULARITIES ON A MAJOR PORTION OF THE SURFACE OF THE CASTING EMERGING FROM THE MOLD AND THAT RATE WHICH PRODUCES DEEP TEARS ON THE SURFACE OF THE EMERGING CASTING. 